This invention relates to a lathe for the interior machining of hollow revolving parts, such as threaded pipe coupling sleeves, for example, which generally are formed with two opposite conical threads.
In the formation of hollow parts with interior machined surfaces of revolution such as conical surfaces, interior machining is advantageously performed on machines of the lathe type. The removal of the metal necessary to produce the interior surfaces, especially threads, is thus performed by cutting tools attached to the end of a tool holding bar or bars having an outside diameter necessarily smaller than the inside diameter of the sleeve to be formed and a length necessarily in excess of the depth of the interior conical surface to be machined. This results in a limitation of the power that can be applied to the tool due to the limited rigidity of the tool holding bar and consequently in a limitation on the rate of metal removal per unit of time. Because of these limitations, the present production costs of machining the interior threads of pipe coupling sleeves in quantity are substantially increased over projected costs where the output of a machine is increased in terms of rate of metal removal.